The present invention relates to a method of making semiconductor devices, in particular, those that include low-k or ultra low-k dielectric layers, which have hydrophobic surfaces when initially deposited.
Semiconductor devices include metal layers that are insulated from each other by dielectric layers. As device features shrink, reducing the distance between the metal layers and between metal lines formed within each layer, capacitance increases. To address this problem, insulating materials that have a relatively low dielectric constant are being used in place of silicon dioxide to form the dielectric layer that separates the metal lines.
Conventional single or dual damascene processes may be used to form metal lines within such low-k dielectric layers, e.g., to generate the structure 100 shown in FIG. 1b. FIG. 1a represents a cross-section of that structure prior to a polishing operation. In that figure, structure 100 includes substrate 101, upon which is formed low-k dielectric layer 102. After a trench has been etched into low-k dielectric layer 102, barrier layer 103 is deposited. In addition to lining the trench, barrier layer 103 extends across surface 104 of low-k dielectric layer 102. Conductive layer 105, which may comprise copper, fills the trench and covers barrier layer 103, where that layer rests on top of surface 104.
After forming the FIG. 1a structure, the excess material deposited on surface 104 must be removed, e.g., by using a conventional chemical mechanical polishing (xe2x80x9cCMPxe2x80x9d) process. Such a CMP operation may generate a structure in which barrier layer 103 and copper layer 105 remain within the trench onlyxe2x80x94as shown in FIG. 1b. Many commercially available rotary and orbital polishers may be used to perform such a CMP step. One example is the Reflexion(trademark) 300 mm CMP system, which is available from Applied Materials, Inc.
After the CMP operation, structure 100 may be covered with thousands of slurry particles that must be removed, along with various metal contaminants. To remove those materials, structure 100 may be subjected to a series of cleaning and scrubbing steps. Many commercially available tools, e.g., the Reflexion system mentioned above, integrate CMP modules with a number of cleaning modules that perform those cleaning and scrubbing functions.
Certain materials that may be used to form low-k dielectric layers (e.g., carbon doped oxides) are hydrophobic. When processing a semiconductor wafer, which is covered by such a hydrophobic layer, through a tool""s post-CMP cleaning modules, water drains off the wafer as it is moved from one module to the next. Any remaining water droplets may migrate to the interface between the conductive layer and the low-k dielectric layer. As those droplets shrink, the concentration of corrosive chemicals present in them may rise significantly. When the conductive layer includes copper, such highly concentrated droplets may corrode the copper. In addition, such rapid water loss may leave a significant amount of organic residue, which may render it difficult to bond the low-k dielectric layer to subsequently deposited materials.
Accordingly, there is a need for an improved process for making a semiconductor device that includes a hydrophobic dielectric layer. There is a need for such a process that converts a hydrophobic surface of such a layer to a hydrophilic one in a relatively simple way. There is a need for such a process that may be used during a post-CMP cleaning operation to reduce corrosion and improve adhesion characteristics. The method of the present invention provides such a process.